The present invention is directed to a medical catheter for the intravascular long-term infusion of medication by implanted or extracorporeal dosage devices, said catheter comprising a tube with a catheter tip composed of a single layer or multiple layers of elastomer, whose external protective layer is composed of a toxicologically faultless and biologically compatible elastic plastic that is soft in comparison to the layer lying therebelow.
Medical working devices which are constructed of multilayer plastic materials are disclosed in U.S. Pat. No. 4,557,959, and German Patent No. 32 04 762.
In long-term infusion of medications, for example insulin, into a body through externally wearable or implantable dosage devices, the output thereof is connected to a catheter, whose opening is preferably placed in the peritoneum and is, thus, intraperitoneally located, or into a large vein and is, thus, an intravenous insertion. Problems, that are related to a reaction of a human body to the foreign body or part, occur in such long-term catheterization. The following three reaction patterns, essentially, will occur:
(a) a connective tissue skin grows from the introduction location of the catheter into the peritoneum or, respectively, the blood vessel or from the point of contact therewith in the direction towards the catheter tip and grows around the tip;
(b) a connective tissue grows in a distal direction proceeding from the catheter tip; and
(c) body cells, macromolecules and tissue particles penetrate into the catheter opening and agglomerate to the walls thereof.
The adhesion of such growth depends, to a particular degree, on the surface roughness. The foreign body reactions are triggered by stimuli of a chemical nature, first by the material alien to the body itself and, secondly, by the infused liquid. Over and above this, a mechanical irritation also occurs, for instance due to the stiffness in the edge of the catheter and this stiffness acts as a trigger. Nothing is known regarding the share of the aforementioned irritative or stimuli effects in the foreign body reaction. However, the growth rate is frequently far faster than the useful life of the implanted dosage device so that a premature function outage with the necessity of a surgical catheter revision will occur.
European Patent No. 0 185 865 discloses an implantable intraperitoneal catheter that, among other things, is suitable for injection of insulin into the human body. In order to avoid blockage due to growth of the body tissue, the catheter tip is provided with exit holes arranged following one another between which disk-shaped spacer elements that project laterally are situated. A particular disadvantage of this known arrangement is that the lateral projecting spacer disk first make the introduction of the catheter more difficult and can injure the inside wall of the vessel during the introduction procedure. A second problem is that it causes vascular growth behind the projecting spacer elements in the stationary condition due to eddy formations of the blood stream in a flowing direction.
U.S. Pat. No. 4,705,501 discloses a catheter of the above-known type, whose distal end can be opened and closed by an inflowing liquid or, respectively, by the counter-pressure of the liquid flowing in the vessel. To this end, the distal end of the catheter is bevelled at such an acute angle that a movable tongue arranged between the obtuse angle of the bevel and the acute angle thereof opens or closes the catheter, dependent on the respective flow conditions. Given catheters that are connected to a dosage pump, such a valve mechanism is superfluous.
U.S. Pat. No. 3,434,869, which was the basis for German Offenlegungsschrift 14 91 682, discloses a method for manufacturing catheters having an improved physiological compatibility, whose surfaces are coated with a layer composed of organo-polysiloxane elastomer. Such a polysiloxane elastomer has silica gel as a filler material. It has been shown that this material reacts with the tissue and blood so that proteins, thrombocytes and, due to the relative rough surface, connecting tissue, as well, will adsorbe thereon.